A proxy payment card (hereinafter simply “proxy card”) is a physical card, similar in appearance to a traditional magnetic stripe payment card (e.g., a credit card or debit card) and readable by a traditional magnetic card reader, but it can emulate one or more other payment cards. For example, a proxy card of a particular cardholder may be configurable to emulate either the cardholder's Visa card or MasterCard for any purchase from any given merchant, according to the cardholder's choice at the time of purchase. A proxy card may include electronics, an emulator coil, and other components to store multiple sets of magnetic stripe data, for e.g., card data for two or more payment cards, and can emulate any one of the sets of stored magnetic stripe data. When such a proxy card is swiped through a magnetic read head of a magnetic stripe card reader, a microcontroller on the proxy card controls the emulator coil, causing the emulator coil to “play back” a set of magnetic stripe data sequentially to an emulator coil on the proxy card. The play back causes the emulator coil to produce a magnetic field, which in turn induces a read signal in the magnetic read head coil. The read signal is then decoded by the magnetic read head to obtain the magnetic stripe data.
The above described play back method emulates magnetic stripe data only when the proxy card is powered on. Thus, at the time of each swipe, a user has to power on the proxy card in order to use the proxy card. Consequently, the proxy card can consume a significant amount of power, which can reduce a battery life of the proxy card. Moreover, the play back speed of the proxy card depends on the speed at which the proxy card is swiped and can lead to decoding error. For example, if a user (e.g., the consumer or the merchant) swipes the proxy card at a swipe speed faster than the play back speed, the magnetic read head may not be able to obtain a complete read signal. Consequently, the user may have to swipe the proxy card multiple times before the magnetic read head can obtain a successful read. That wastes both the consumer's and the merchant's time and causes annoyance to both of them.